Explosion-proof asbestos-cement shapes

ABSTRACT

ASBESTOS-CEMENT SHAPES ARE FORMED FROM A FURNISH CONTAINING A SMALL QUANTITY OF VEGETABLE FIBERS DISTRIBUTED THEREIN, THE SHAPES BEING FORMED BY SCREW EXTRUSION,THEREBY PROVIDING ARTICLES OR SHAPES IN WHICH FIBERS EXTEND RANDOMLY FROM THE EXTERIOR SURFACE OF THE SHAPES INTO THE INTERIOR REGIONS THEREOF AND THUS PROVIDE &#34;BLEED&#34; CHANNELS THROUGH WHICH VAPOR FORMED IN THE INTERIOR MAY ESCAPE WHEN THE SHAPES ARE SUBJECTED TO HEATING, WITH CONSEQUENT SUBSTANTIAL ELIMINIATION OF TENDENCY TO EXPLODE.

ke-vz \i ilnited States Patent 015 3,667,977 Patented June 6, 19723,667,977 EXPLOSION-PROOF ASBESTOS-CEMENT SHAPES James E. Harbison,Ambler, Pa., assignor to Certain- Teed Products Corporation, Ardmore,Pa. No Drawing. Filed Feb. 6, 1970, Ser. No. 9,423 Int. Cl. C04b 31/08US. Cl. 106-99 3 Claims ABSTRACT OF THE DISCLOSURE Asbestos-cementshapes are formed from a furnish containing a small quantity ofZegetable fibers distributed therein, the shapes being formed by screwextrusion, thereby providing articles or shapes in which fibers extendrandomly from the exterior surface of the shapes into the interiorregions thereof and thus provide bleed channels through which vaporformed in the interior may escape when the shapes are subjected toheating, with consequent substantial elimination of tendency to explode.

This invention relates to explosion-resistant asbestoscement shapes,especially adapted for use as structural members, pipes and the like,and to a method for manufacturing such explosion-resistant shapes.

It is known that when asbestos-cement shapes are subjected tosubstantial and rapid heating, they exhibit a marked tendency toexplode, shatter or break up. For example, when a building such as ahouse formed of or containing asbestos-cement structural parts issubjected to fire, for instance a fire in the contents of the house, thehigh temperature to which the asbestos-cement shapes are subjectedresults in evaporation of moisture contained within the mass of theshape. This heating, especially if it is relatively rapid, frequentlycauses the shape to literally explode or break apart, often withresultant violent scattering of fragments of the shape over substantialdistances. This effect is hazardous not only to properly, but also topersons within close range.

The present invention is concerned with asbestos-cement shapesespecially suitable for use as structural components of buildings inwhich tendency to explode is substantially eliminated and in which thisis accomplished without appreciable loss of strength or other desirablephysical characteristics of the asbestos-cement material of which theshapes are formed. In general, this is accomplished according to theinvention in consequence of the use of fibers of a certain type in thefurnish from which the shape is made, and also in consequence of the useof a certain particular manufacturing technique for forming the shapesfrom the fiber containing furnish.

First, with reference to the fibrous material, it is contemplated toemploy a small percentage of vegetable fibers preferably wood fiberswhich are characterized by relatively great freeness. Free'ness is aterm used with respect to fibers, especially wood fibers, employed inthe manufacture of paper, roofing felts, fibrous hardboard or fibrousinsulating board. In general relatively great freeness indicates thatthe fibers will drain freely when mixed with water to prepare a pulp. Amore specific freeness test is referred to more fully hereinafter.

According to the present invention, a small percentage of wood fibers,for instance about 0.7% by weight of the dry ingredients, is added toand mixed with the other ingredients of the asbestos-cement furnish. Thewater required is then added and the shapes or articles are formed fromthe resultant mixture.

Although asbestos-cement shapes, pipes or the like may be made from sucha mixture by a va'i'iety of different techniques, it is hereincontemplated that the articles be prepared by screw extrusion of thefurnish, the extrusion being carried out promptly after the water hasbeen added to the dry ingredients, and the shapes being cured afterdelivery from the nozzle of the extruder.

An important reason for the preference for the use of screw extrusionaccording to the present invention is that this type of fabricationresults in a type of distribution of the fibers throughout the mass ofthe article being made such that many of the fibers have one endadjacent to an exposed surface of the shape and the other end located inthe interior of the article. Although extrusion has a tendency to causesome fiber orientation in certain areas or zones, the fiber orientationand distribution is nevertheless three-dimensional in character, withthe result that many fine channels are provided in the interior of thematerial terminating in pores at the surface of the article. Suchchannels, even through occupied by the fiber itself, neverthelessrepresent flow paths through which vaporgenerated in the interior maypass to the surface of the article and thus be liberated without development ofinterior localized areas of high pressure such as to causeexplosion.

In contrast to the foregoing, with certain other known techniques forforming shapes from asbestos-cement furnish or mixes, vegetable fibresof the kind herein contemplated for use would have a tendency tostratify or to become concentrated in localized areas. For example withtypes of fabricating operations in which lamination is employed to forman article, the overwhelming bulk of fibers, if present, would tend tolie in planes paralleling the planes of lamination.

It is therefore of importance according to the present invention notonly to utilize vegetable fibers but also to form the shapes or articlesby screw extrusion, since by the use ofsuch extrusion, the distributionand random orientation of the fibers is maximized, with the result thata smaller total quantity of fibers may be employed, thereby providingthe highly desirable explosion-proof characteristic while minimizingloss of strength and other desirable physical properties.

Although it has been known to employ sawdust and even certain fibrousmaterials in cement mixes'of various kinds for various purposes, it isimportant in the practice of the presentinvention to utilize fibers ofrelatively great freeness, as already indicated above, and to employsuch fibers in only very low concentration. A fiber content of from0.10% to 2.00% by weight of the dry ingredients is usable, mostadvantageously from about 0.25% to about 1.0%. These percentages arehere given on the basis of the weight of the dry ingredients used inmaking up the furnish. However, when an article is made from such afurnish, the percentage of the fibrous material will be essentially thesame in the ultimate cured or dried article, because the addition ofwater and the subsequent curing only alters the weight by a small amountas compared with the initial dry ingredients.

Although vegetable fibers of different types may be utilized, woodfibers are preferred, and the wood fibers used may be of the same typeas employed in making roofing felt, insulating fiberboard or hardfiberboard. Fibers utilized for 'such purposes have much greaterfreeness than do the wood fibers employed in the manufacture of paper.As a specific test of the freeness of the fibers preferably usedaccording to the present invention, after preparing a slurry or pulp byadding the fibers to water, the fibers may be placed upon a screen orpositioned in some other manner to permit free drainage, and the fibershave a degree of freeness usable according to the invention if theyreadily drain down to less than 70% water content by weight. Mostadvantageously, the fibers should readily drain down to a water contentat least as low as 3 50%. At any point below the 70% level, the fiberscan be handled as a solid, rather than as a slurry, and this is ofimportance from the standpoint of facilitating and enhancing the fiberdistribution and random orientation contemplated by the invention.

The relatively great freeness of the fibers as referred to facilitatespreparation of the furnish because such fibers may readily be mixed inthe same manner as a dry ingredient.

The furnish should contain both asbestos and cement and may also containother ingredients if desired, for instance silica. In any event, thecement should constitute at least about 40% by weight of the dryingredients and may even run up to about 85 or 90% of the dryingredients. The asbestos should constitute from about 5% to about 60%by weight of the dry ingredients. In general the Portland cements aresuitable for the purposes ofv the present invention, especially thoseknown to the trade as Types I, II, HI and III-A in their normal powderform.

Although a variety of types of asbestos fibers may be employed, any ofthe seven grade fibers are preferred, a typical and especiallyadvantageous type being Canadian Quebec chrysotile slip fiber.

The furnish may be prepared for extrusion in the manner referred to incopending application of Joseph L. Cangelosi and Frederick E. Hawkins,Ser. No. 767,892 filed Sept. 9, 1968, now issued as Pat. No. 3,529,981,Sept. 22, 1970, and assigned to the assignee of the present application.Specific compositions of furnish as referred to in said copendingapplication may here be utilized, but with the addition of a smallpercentage of the fibers contemplated for use according to the presentinvention.

A comparative example indicating a formulation both with and without thefibrous material is indicated just below:

EXAMPLE A Percent Portland cement 4 6 /9 Silica 31 Asbestos fiber 22%EXAMPLE B Percent Portland cement 46.2 Silica 30.8 Asbestos fiber 22.3Wood fiber .7

It will be seen that these formulations are identical except for theaddition of the wood fibers in Example B.

After the addition of the same quantity of water to each (about 25pounds for each 100 pounds of the dry ingredients), building componentswere extruded from these two formulations and the components weresubjected to astandard fire test (ASTM Test Ell9-67), in which thecomponents were subjected to a temperature of 1500 F. The componentsmade from the formulation of Example A exploded and the components madefrom the formulation of Example B did not explode.

I claim:

1. An asbestos-Portland cement extrusion having from about 0.25% to1.00% by weight of fibrous material dispersed therein, the fibrousmaterial consisting of vegetable fibers characterized by freenesssufficient to readily drain to less than 70% of water content, and thefibers being distributed and randomly oriented throughout the mass ofthe extrusion to define a plurality of fine fibershaped channels throughwhich vapors may flow from the interior of said extrusion to itssurface.

2. An asbestos-cement extrusion as defined in claim 1 in which thefibrous material comprises wood fibers.

3. An asbestos-cement extrusion consisting essentially of from about 40%to 85% by weight of Portland cement and from about 5% to by weight ofasbestos, and having from about 0.10% to 2.00% by weight of fibrousmaterial dispersed therein, the fibrous material consisting essentiallyof wood fibers characterized by freeness sufficient to readily drain toless than of water content, and the fibers being distributed andrandomly oriented throughout the mass of the extrusion to define aplurality of fine fiber-shaped channels through which vapors may flowfrom the interior of said extrusion to its surface.

References Cited UNITED STATES PATENTS 3,529,981 9/1970 Hawkins et a1.l0699 2,144,213 1/1939 =Bassett et al. l0699 1,314,772 9/ 1919 Viensl0699 1,961,525 6/ 1934 Ofiutt l0699 889,569 6/ 1908 Albrecht l0699JAMES E. POER, Primary Examiner W. T. SCOTT, Assistant Examiner US. Cl.X.R. 106-93

